There is no doubt that the incidence of congestive heart failure (CHF) in the Western world is increasing as the population ages. The NHLBI has estimated that more than 2 million Americans have heart failure, with about half a million new cases diagnosed each year. The general objective of this proposal is to understand the role of vascular oxidative stress in CHF. The central hypothesis is that the reduced wall shear stress (WSS) in the microcirculation and reverse flow in the larger vessels will increase O2- production largely mediated by the NADPH oxidase system and hence reduce the vascular bioavailability of NO. This upregulation of NADPH oxidase is thought to be mediated through changes in endothelial cytoskeletal loading and deformation. To test this and other hypotheses, we set the following five Specific Aims: 1) To document and state the physical loading (blood flow, pressure and WSS) acting on the blood vessel endothelium in awake, free ranging animals precisely and analytically during the progression of CHF; 2) To identify the role of low and negative WSS determined in Aim 1 as the initial stimuli for O2- production in ex vivo vessels during acute flow reduction and flow reversal; 3) To establish the remodeling of the balance between NO and O2- chronically during the progression of HF due to reduced flow in the microcirculation and increased flow reversal in the macrocirculation identified in Aims 1 and 2; 4) To elucidate the role of NADPH oxide as well as other regulatory enzymes for NO (eNOS) and O2- dismutase (SOD) in limiting NO bioavailability in Aim 3; and 5) To quantify the endothelial and smooth muscle cell dysfunction of blood vessels due to the oxidative imbalance in Aims 2-4. The recorded in vivo blood pressure, flow and WSS data will be characterized with the empirical model decomposition method during the progression of CHF. The hemodynamic measurements will be correlated with the production of NO metabolites and expression of eNOS and SOD. The contribution of this project is to mathematically characterize the non-stationary, nonlinear, and stochastic features of the blood flow and blood pressure, the shear stress acting on vascular endothelial cells, and to show how escalation of low and negative WSS can have a detrimental effect on endothelial function, superoxide production, SOD and eNOS expression.